Field of the Invention
The invention relates to a resonant high current density transformer, and more particularly, to a reduced-sized resonant transformer capable of increasing power density and easy of automated processing.
Description of the Related Art
In power supply system for electronic products such as LCD TVs, a main type of transformers used is transformers with leakage inductance property (such as LLC transformer) that reduces switching loss and noise.
In TW Utility Patent Publication No. M333646 titled “Improvement of Leakage-Inductance-type Resonant Transformer”, the transformer mainly includes: an outer bobbin provided with a first through-hole and a first recessed hole; an inner bobbin fitted inside the first through-hole of the outer bobbin, the inner bobbin being provided with a second through-hole and a second recessed hole; a core assembly with a first core, a second core and a third core, wherein the first and second cores are disposed in the second through-hole of the inner bobbin and the third core is disposed in the first recessed hole of the outer bobbin and the second recessed hole of the inner bobbin. By fitting the inner bobbin into the first through-hole of the outer bobbin, the coils in a first winding region and the coils in a second winding region can be overlapped to increase coupling. In addition, since the outer bobbin is provided with the recessed hole, heat generated from the coils of the inner bobbin can be effectively dissipated. Further, by providing the third core in the recessed holes, magnetic lines are able to form a sub-loop that increases the leakage inductance.
In addition, in TW Patent Publication No. I416553 titled “LLC Transformer Structure”, the transformer includes: a first winding base including: a body with a first winding region and a plurality of single-slot second winding regions, the first winding region having a plurality of guide pins, and the plurality of single-slot second winding regions being disposed at either side of the first winding region, the body having a first sidewall and a second sidewall on two opposite sides, and each of the first and second sidewalls having an opening; and a first channel running through the body; a primary winding wound on the first winding region of the first winding base and connected to the plurality of guide pins; a plurality of secondary winding wound on the plurality of single-slot second winding regions of the first winding base; a cover having a second channel, the second channel being in communication with the openings of the first and second sidewalls when the cover and the first winding base are being assembled together; and a magnetic core assembly partly provided in the first channel of the first winding base and the second channel of the cover.
By providing a plurality of single-slot second winding regions for winding a plurality of secondary windings separately, the windings and magnetic paths can be modified, and the size of the transformer can be reduced. In addition, the problem with a lack of control of the leakage inductance in the conventional transformer due to an air gap formed between the primary and secondary windings during the assembly of the magnetic core assembly can be eliminated.
However, the above two transformer designs still present the following shortcomings:
1. Conventional LLC transformer are usually formed by winding traditional wires (enameled wires) on the primary and secondary sides, but in the case of high current output, multi-strand secondary winding structure are often used to achieve a higher current tolerance. However, with these winding structures with multi-strand wires (enameled wires), it can be difficult to strip off the insulation layers, there might also be difficulties in output wiring or wire twisting due to the large number of strands. Furthermore, gaps are created between wires (enameled wires), so the size of the transformer cannot be reduced.
2. In conventional LLC transformer structures, the primary and secondary windings are wound on different locations of a single bobbin (winding base), in addition to winding, interspersing insulation sleeves and twisting wires are labor intensive.
3. In conventional LLC transformer structures, there is an approach of using metal plates to replace the secondary winding. However, if the primary and secondary windings are provided on the same bobbin, distances associated with safety regulations may not be long enough, and leakage inductance cannot be easily modified, so an additional inductor is needed as a resonant inductor. On the other hand, if the primary and secondary windings are provided on the two bobbins, a constant distance between the two bobbins is difficult to maintain, which results in drifts in characteristics such as the leakage inductance.
In view of the shortcomings in the conventional transformer structures, the present invention is proposed to provide improvements that address these shortcomings.